Passive mountings comprise a passive spring element, such as an elastomer section, and attach between an engine and structure to isolate vibration therebetween. Examples of passive mountings are described in commonly assigned U.S. Pat. Nos. 5,351,930, to Gwinn et al., 5,176,339, to Schmidt et al. and 5,108,045, to Law et al. Passive mountings have the disadvantage that annoying and/or noise-producing vibration cannot, in general, be completely eliminated.
Fluid mountings are generally described in LORD.RTM. Technical Article LL-2166 entitled "Understanding Hydraulic Mounts for Improved Vehicle Noise, Vibration and Ride Qualities" by W. C. Flower. Commonly assigned U.S. Pat. No. 4,811,919 to Jones describes a fluid mounting which incorporates a volume compensator. Other examples of fluid mountings may be found in commonly assigned U.S. Pat. Nos. 5,413,320 to Herbst, 5,374,039 to Schmidt et al., and 5,197,692 to Jones et al. Fluid mountings are, in essence, tunable passive devices which use a fluid to add additional damping or tuned-fluid "inertia" effects. Fluid mountings have the disadvantage that although they provide improved isolation, as compared with passive mountings, they are generally only effective within a relatively narrow frequency range.
Active fluid mountings which attach between a structure and engine for actively isolating vibration therebetween are generally known. Commonly assigned U.S. Pat. No. 5,427,347 to Swanson et al., describes an active fluid mounting apparatus which may use a simple feedback control. Commonly assigned U.S. Pat. No. 5,174, 552 to Hodgson et al. describes another active fluid mounting. Further examples of active fluid mountings are found in U.S. Pat. Nos. 5,439,082 to McKeown et al., 5,333,455 to Yoshioka, 5,238,232, to Kobayashi et al., 5,116,029 to Gennesseaux, 5,067,684 to Garnjost, 4,693,455 to Andra, and 4,638,983 to Indigkeit et al.
However, none of these prior art mountings provide a compact active fluid mounting which can be controlled to isolate vibration over a wide frequency range and which addresses the need for easy change out of the active portion when its useful life is met, i.e., when refurbishment is required or to easily adjust the output characteristics, and/or to allow interchangeability of the active mounting for multiple application platforms.